Pretty sure cod liver oil has vitamin A. Used to be a treatment for measles and rickets and others because of its vitamin A contents.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2258476/

https://www.westonaprice.org/did-cod-liver-oil-contribute-to...

Sorry, maybe it was a misunderstanding, especially since the Vikings were mentioned on the thread.

I was thinking about this: https://en.wikipedia.org/wiki/Cod_liver_oil